Conventionally, as described in JP-A No. 2007-147128, there has been a heat exchanger where plural flat tubes disposed in multiple tiers along a predetermined tube tier direction are disposed in multiple rows so as to be adjacent to each other in a tube row direction intersecting the tube tier direction and the longitudinal direction of the flat tubes and where one end portions in the longitudinal direction of the flat tubes adjacent to each other in the tube row direction communicate with each other via a coupling header. Here, as the coupling header, a structure is disclosed where intermediate plates, in which are formed communicating holes for forming coupling passages that allow the one end portions in the longitudinal direction of the flat tubes adjacent to each other in the tube row direction to communicate with each other, are inserted into and joined to the inside of a square pipe-shaped main plate in which are formed through holes for inserting the flat tubes.